Automatic document feeder having a document shunting path

ABSTRACT

In an automatic document feeder for use in an image forming device such as copy machine and facsimile machine: a document shunting path for temporarily shunting a document is provided at an upstream side of a document reading portion; in a different-size mixed mode where different sizes of documents are placed in a mixed manner, the leading edge and rear edge of the document are detected by a sensor during conveyance of the document in the direction toward the document reading portion, so that the length of the document is detected; thereafter the document is conveyed in the reverse direction so that the rear edge of the document is shunted into the document shunting path; and thereafter the document is again conveyed in the forward direction to conduct reading. Thus, it becomes unnecessary to provide a longer conveyance path for detecting the length of the documents, so that the size of the feeder itself can be reduced.

This is a division of application Ser. No. 09/688,632 filed

Oct. 16, 2000 now U.S. Pat. No. 6,585,258, which is a division ofapplication Ser. NO. 09/095,271 filed Jun. 10,1998, now U.S. Pat. No.6,145,834 issued Nov. 14, 2000.

BACKGROUND OF THE INVENTION

The present invention relates to an automatic document feeder which isadopted in an image reading apparatus such as a copy machine orfacsimile machine.

BACKGROUND ART

In a conventional automatic document feeder such as disposed on a copymachine body, there has been generally adopted such a constitution thatthe documents placed on a document tray are automatically fed andconveyed sheet by sheet toward reading means on the copy machine body,and the fed document is read by an optical system in the copy machinebody and then conveyed toward a discharge portion (see, JapaneseUnexamined Patent Publication No.8-133551, as a similar technique).

Relatedly, it is necessary to previously inform the copy machine body ofinformation about the document size, before reading the document fedfrom the document tray. Conventionally, there have been arranged aplurality of detection sensors along the document feeding direction inthe document tray, and the length of documents have been detected bymeans of on/off operation of the detection sensors upon placement ofdocuments onto the tray.

However, in the detection means as described above, when the documenttray is fed with different sizes of documents in a mixed manner, thedetection sensors are caused to constantly detect the maximum size amongthe mixed documents, causing such a problem that the information ofdocument size is not accurately obtained.

As such, there has been also conventionally proposed a constitution thatthe detection sensors are arranged on a conveyance path extending fromthe document tray up to the document reading portion which is opposed tothe reading means of the copy machine body and the size of eachdocuments, which are fed from the document tray sheet by sheet, isdetected on the conveyance path before the image on the document isread.

However, in such a method that the document size is detected on theconveyance path, as described above, there is required a long conveyancepath which is commensurate with the possibly maximum size of document(such as A3 size of document placed in a lengthwise direction), causinga problem that the size of automatic document feeder is increased.

It is therefore an object of the present invention to provide anautomatic document feeder which can assuredly detect the document sizeeven by a shortened conveyance path before the image on the document isread, without increasing the size of the feeder itself.

Further, in a conventional automatic document feeder, there has beenproposed a feeder capable of reading images on the double sides of thedocument. This feeder is constituted such that the document fed from adocument tray is wound on a large sized conveying roller, conveyed to adocument reading portion opposite to a reading means of a copy machinebody to be read the front surface thereof in the document readingportion by the reading means of the copy machine body. After that, thedocument is then reversed by means of a switchback path provided on thedownstream side, then the document is conveyed on the periphery of theconveying roller to be read the back surface of thereof and at the sametime the document is again reversed by means of a reverse discharge pathto be discharged on a discharge tray after page arrangement.

However, such an automatic document feeder as described above shouldprovide both of the switchback path and the reverse discharge path,therefore, there is the problem that the path or feed mechanism becomescomplex, resulting in a large sized automatic document feeder. On theother hand, if these two paths are combined into a single path, a radiusof curvature of this single path should be made small, resulting ininsufficient document conveyance effect.

Moreover, when the document is fed from the switchback path to theconveyance path, the leading edge of the document is aligned using theconveying roller. However, if a distance from the switchback path to aresist position is long as conventionally, since a distance wherein thedocument slidingly contacts with the periphery of the stopped conveyingroller becomes longer, there is a fear that the document cannot beconveyed satisfactorily due to friction with the periphery of theconveying roller.

According to the present invention, the path structure and feedingmechanism are made simple to achieve the minimization of the automaticdocument feeder itself.

Further, according to the present invention, the radius of curvature ofthe document discharge path is made small to obtain a sufficientdocument conveyance effect.

Moreover, according to the present invention, the reversed documentconveyed from the switchback path can be reliably aligned without aninfluence of the periphery friction of the conveying roller.

In the above described Japanese Unexamined Patent Publication No.8-133551, there has been proposed such a constitution of a book mode forreading the document put on a platen other than a sheet through modefrom reading the document being conveyed. In particular, in order tominimize the apparatus, a switchback path used for reading the doublesides of the document by reversing the document, and a switchback pathfor reversing again the document of which double sides have been read todischarge to a discharge tray after page arrangement are furtherprovided between the discharge tray and a platen cover.

However, in a case that a switchback path is provided between thedischarge tray and the platen cover as described above, there is anecessity for pulling out the document from a narrow space between thedischarge tray and the platen cover when a jam occurs, resulting indifficulty in a jammed document treatment.

According to the present invention, in an apparatus in which thedocument conveying path, such as a switchback path, is provided betweenthe discharge tray and the platen cover, a document jammed in thedocument conveying path can be easily treated.

In an automatic document feeder, in order to align the document to beconveyed during the conveying process of the document fed from thedocument tray, it is necessary to provide a resist roller to feed thedocument to the reading means of the copy machine body after abuttingthe leading edge of the document to the resist roller thereby aligningthe document. Conventionally, there is proposed an automatic documentfeeder in which a resist roller is disposed so as to be in pressurecontact with a conveying roller, in order to reduce the conveying pathfrom the document tray to the resist roller, so that the document fedfrom the feeding roller is abutted to the pressure contact portionbetween the conveying roller and the resist roller to thereby bealigned.

However, with such a constitution as described above, the conveyingroller should be stopped at the resist time in order align the documenton the conveying roller. Also, the next document cannot be fed to theresist position unless the conveyance of the preceding document iscompleted. Accordingly, intervals for feeding the document arelengthened, resulting in a long document treatment time.

Accordingly, it is an object of the present invention is to divide theprocess of document conveyance by means of the conveying roller from thealigning to thereby reduce the document treatment time.

SUMMARY OF THE INVENTION

To solve the aforementioned problems, the present invention provides anautomatic document feeder comprising:

a document feeding portion for placing documents thereon;

document reading means for reading the documents;

a document discharging portion;

a document conveyance path connecting among the document feedingportion, the document reading portion and the document dischargingportion;

a conveying roller, which is capable of forwardly rotating and reverselyrotating, for conveying the documents along the document conveyancepath;

a document shunting path branched from the document conveyance path;

first detection means for detecting a leading edge and a rear edge ofthe document; and

second detection means, which is disposed in the document conveyancepath on the downstream side of the first detection means, for detectingthe leading edge of the document; and

wherein the conveying roller is forwardly rotated to convey the documentwith the leading edge thereof headed, and, after the rear edge of thedocument is detected by the first detection means, the conveying rolleris reversely rotated to move the rear edge side of the document into thedocument shunting path, until the leading edge of the document is movedback to a position on the upstream side of the document reading portion.

Further, the present invention provides an automatic document feedercomprising:

a document feeding portion for placing documents thereon;

document reading means for reading the documents;

a document discharging portion;

document conveying means for conveying the documents;

a document conveyance path for conveying the documents from the documentfeeding portion to the document reading portion or from the documentreading portion to the document discharging portion;

a document shunting path branched from the document conveyance path; and

document size detection means for detecting a document size by detectingthe leading edge and the rear edge of the document;

wherein the document is conveyed to the document shunting path beforebeing read by the document reading means, then the leading edge of thedocument is conveyed to the upstream side of the document reading means,and the document size detection means detects the document size whilethe document is conveyed from the document feeding portion through thedocument reading means.

According to such a constitution, it is unnecessary to provide a longerconveyance path of documents such as in the conventional, therebyminimizing the size of the document feeder and also detecting accuratelythe document size.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of an automatic document feederaccording to the present invention;

FIG. 2 is an enlarged view of an essential part of the automaticdocument feeder according to the present invention;

FIG. 3 is an enlarged view of a structure in the vicinity of a documentreversing portion;

FIG. 4 is an enlarged view of a aligning state in the vicinity of theexit of the document reversing portion;

FIG. 5 is an enlarged view of a discharge path from the documentreversing portion to the document discharging portion;

FIG. 6 is a timing chart for feeding the document, in one side readingin a normal mode;

FIG. 7 is a timing chart for conveying and discharging the document, inone side reading in the normal mode;

FIG. 8 is a timing chart for conveying and discharging the document, indouble side reading in a normal mode;

FIG. 9 is a timing chart for feeding the document in a different-sizemixed mode;

FIGS. 10(a)-10(c) are explanatory views showing the motion of thedocument in one side reading in a normal mode;

FIGS. 11(a)-11(c) are explanatory views showing the motion of thedocument in front surface reading in a double-side reading mode;

FIGS. 12(a)-12(c) are explanatory views showing the motion of thedocument in back surface reading in the double-side reading mode;

FIGS. 13(a)-13(c) are explanatory views showing the motion of thedocument in feeding of the document in the different-size mixed mode;

FIG. 14 is a sectional view of an internal structure of the documentreversing portion;

FIG. 15 is a sectional view of a state when a platen cover is opened;

FIG. 16 is an enlarged perspective view of circled portion A in FIG. 14;

FIG. 17 is a sectional view along 17—17 of FIG. 16;

FIG. 18 is an enlarged perspective view of circled portion C in FIG. 14;

FIG. 19 is a schematic sectional view of another automatic documentfeeder according to the present invention;

FIG. 20 is a perspective view of a resist portion of the automaticdocument feeder in FIG. 19;

FIG. 21 is a timing chart in a one-side reading mode; and

FIG. 22 is a timing chart in a double-side reading mode.

DESCRIPTION OF THE PREFERRED EMBODIMENT

There will be described hereinafter in detail an embodiment of anautomatic document feeder according to the present invention, withreference to the accompanying drawings.

In the drawings, reference numeral 1 designates an automatic documentfeeder according to the present invention, which comprises: a documenttray 2 for placing the documents thereon; document picking-up means 4arranged adjacent to a document feeding opening 3; a document feedingpath 6 extending from the document feeding opening 3 up to a documentreading portion which faces to document reading means 5 of a copymachine body H; a resist roller 7 provided on the way of the documentfeeding path 6 to thereby align the leading edge of the document;conveying means 8 for conveying the aligned document to the documentreading portion; a document discharging portion 9 for discharging thedocument read by the document reading means 5; and document reversingportion 10 provided between the document reading portion and thedocument discharging portion 9. Each of the documents placed on thedocument tray 2 is fed sheet by sheet to the document reading portion,and the document is discharged to the document discharging portion 9after its front surface is read; or switched back at the documentreversing portion 10 after its front surface is read, and again fed tothe document reading portion by the conveying means 8 to thereby readthe back surface of the document.

The copy machine body H is provided with: a transparent glass 11 usedfor reading the image on the document by the document reading means 5when the document is automatically fed; and a platen 12 used forcarrying a document such as book, to thereby read the same.

The document tray 2 is arranged obliquely toward the document feedingopening 3 of the feeder body, and is provided with a guide plate 13moveable in the width direction of the documents. The width of documentsis detected by the position of this guide plate 13. Further, thedocument tray 2 is provided with two size detection sensors S1 fordetecting the length of the document in the feeding direction. Thesesize detection sensors S1 may comprise, for example, a limit switch oroptical sensor. In case of a normal mode where all the documents placedon the document tray 2 have the same sizes, the size detection isperformed by means of the guide plate 13 and the size detection sensorsS1. In case of a “different-size mixed mode” where different sizes ofdocuments are placed in a mixed manner, the size detection of documentsis performed by means to be described later, without utilizing the guideplate 13 and size detection sensors S1.

The document picking-up means 4 is arranged near the document feedingopening 3, and comprises: a feeding roller 14 displaceable in thethickness direction of the documents placed on the document tray 2; anarm 15 for rotatably supporting the feeding roller 14; and a separationroller 16 positioned at the other end of the arm 15. The feeding roller14 is normally held in a stand-by position, and moved from the stand-byposition toward a feeding position by the operation of a feeding clutch17 a, whereafter the roller 14 is rotated by following the rotation ofseparation roller 16 to thereby feed the documents on the document tray2 sheet by sheet. There is rotated the separation roller 16 via feedingclutch 17 b which operates upon reverse rotation of a feeding/reversingmotor 18, so that the documents are separated between separation patssheet by sheet and thereafter fed to the document feeding path 6.

Arranged near the downstream side of the separation roller 16 is aresist sensor S2, and a resist roller 7 is arranged near the downstreamside of the sensor S2. The resist sensor S2 detects the leading edge ofthe document in the normal mode, and the rear edge of document inaddition to its leading edge in the different-size mixed mode. In thedifferent-size mixed mode, the document size is determined by obtainingthe document length based on the leading edge signal and rear edgesignal which are detected by the resist sensor S2. The resist roller 7comprises a driving roller 20 and a driven roller 21, and the drivingroller 20 is rotated at a predetermined timing by the forward rotationof the feeding/reversing motor 18. After the leading edge of thedocument abuts the resist roller 7 so that the leading edge is aligned,the driving roller 20 is rotated after waiting a predetermined time, tothereby pinch the document cooperatively with the driven roller 21 toconvey the document into the document feeding path 6.

The conveying means 8 comprises: a conveying roller 22 for revolvinglyconveying the document; and pinch rollers 23, 24 arranged on theperiphery of the conveying roller 22. The document is gripped betweenthe conveying roller 22 and the pinch rollers 23, 24, and fed to thedocument reading portion which is opposed to the document reading means5. The rotational direction of the conveying roller 22 is switched bythe forward and reverse rotations of a pulse motor 25.

There is disposed a lead sensor S3 at the upstream side of the documentreading portion. In the normal mode, this lead sensor S3 is utilized todetect the leading edge of the document, and the rotation of theconveying roller 22 is stopped based on the detection signal from thesensor S3 to thereby hold the document in a reading stand-by state. Inthe different-size mixed mode, the sensor S3 also detects the leadingedge of the document which is being reversely conveyed (i.e., the rearedge in the conveying direction during the reverse conveyance). Theforward conveyance of the document is resumed based on the reading startsignal supplied from the copy machine body H. The reading of document isperformed by the document reading means 5 when the document passes overthe surface of the transparent glass 11.

The document reversing portion 10 is positioned downstream of thedocument reading portion, and comprises: an introducing guide 27 with anopening thereof being flared; and a pair of reversing rollers 28disposed near the guide 27; and a switchback path 29 provided at therear side of the rollers 28. As shown in FIG. 3, pinch rollers 30 and 31are provided at an inlet end and an outlet end of the introducing guide27, respectively, to thereby promote the conveyance in a documentdischarge path 32 and the conveyance and discharge of document into andfrom the document reversing portion 10. Particularly, the pinch roller31 at the outlet end also has a function as a reverse resist at the timeof rear surface reading of the document G. That is, the pinch roller 31which is in pressure contact with the conveying roller 22, rotatestogether with the conveying roller 22 by driving the conveying roller22. But, at the time of aligning, the rotation of the conveying roller22 is stopped to abut the leading edge of the document G to a pressurecontact position 50 between the pinch roller 31 and the conveying roller22, thereby aligning the document G. Thus, since the reverse resist iscarried out at the outlet end of the document reversing portion 10, theleading edge of the document G is not in sliding contact with theperiphery of the conveying roller 22. The reversing rollers 28 areopened and closed by a solenoid 33, and are adapted to rotate in theforward and reverse directions by means of the feeding/reversing motor18, so that the document is reversely fed after switching back theconveyance direction of the document from its leading edge to its rearedge by the forward rotation and reverse rotation of the reversingrollers 28. There is disposed a reverse sensor S4 near the reversingrollers 28.

The document discharging portion 9 is disposed under the document tray2, and comprises: upper and lower paired guides 35 which continuouslyextend from the document discharge opening; a pair of documentdischarging rollers 36 provided on the way of the guides 35; and adischarge tray 37. The document discharging rollers 36 are adapted torotate in the forward and reverse directions by means of the pulse motor25. Disposed near the document discharging rollers 36 is a documentdischarge sensor S5 for detecting the discharge of document.

Around the conveying roller 22, there are provided a flapper 38 near theinlet of the document reversing portion 10, and a flapper 39 near theinlet of the document discharging portion 9, respectively, for switchingthe conveyance direction of the document. The former flapper 38, asshown in FIG. 3, is disposed in the introducing guide 27 which is putbetween the pinch rollers 30 and 31, and switches the conveyance path ofthe document to a path on the side of the document reversing portion asshown in FIG. 3 and to a path on the side of the discharge path 32 asshown in FIG. 5. A control flapper 53 which is hanging down due to itsweight, is rotatably provided on one side of a rotation shaft 52 of theflapper 38, on the other side of the rotation shaft 52, a guide piece 54which rotates integrally with the control flapper 53, is provided. Thisguide piece 54 is abutted to the leading edge of the document whenfeeding the document from the document reversing portion, to therebyintroduce the document to the pressure contact position 50 between theconveying roller 22 and the pinch roller 31. Thus, the leading edge ofthe document can be prevented from slidingly contacting the periphery ofthe conveying roller 22. Additionally, in this embodiment, since theguide piece 54 rotates integrally with the control flapper 53 which ishanging down due to its weight, as shown in FIG. 3, the guide piece 54rises due to the weight of the control flapper 53 when the document isreversed, thus the leading edge of the document G can be easilyintroduced to the pressure contact position 50. Further, as shown inFIG. 4, after the leading edge of the document G reaches the pressurecontact position 50, a little document loop is formed between the guidepiece 54 to press the guide piece 54 onto the conveying roller 22, andat the same time, there occurs a force to press back the guide piece 54due to the weight of the control flapper 53. Therefore, the leading edgecan be further contacted with the pressure contact position 50 tofurther improve the alignment effect.

The flapper 39 provided near the downstream side of the pinch roller 31is used for switching the document between the document feeding path 6and the document discharging portion 9. The switching of this flapper 39is made together with the flapper 38 by means of a solenoid 40.

In this embodiment, there is formed a document shunting path 41 in thedocument feeding path 6 between the resist roller 7 and the pinch roller23 being pressed onto the conveying roller 22, in which the path 41 isdownwardly branched from the document feeding path 6. This documentshunting path 41 is defined by a flapper 42 which is normally urgedupwardly by a spring so that a distal end of flapper 42 projects intothe document feeding path 6, and a guide plate 43 which forms a shuntpath having a curved shape cooperatively with the lower surface of theflapper 42. The flapper 42 is pushed downwardly, when the document isconveyed thereon, to sink from the document feeding path 6. The distalend of flapper 42 projects into the document feeding path 6, when nodocuments are being conveyed thereon, to open the shunt path.

There will be explained hereinafter the automatic reading of document bymeans of the automatic document feeder having the aforementionedconstitution, with reference to the timing charts shown in FIGS. 6through 9 and the motional views of the document shown in FIGS. 10(a)through 13(c).

Firstly, there is explained one side reading in a normal mode wheredocuments having same sizes are placed on the document tray 2, withreference to FIGS. 6, 7 and 8. As shown in FIGS. 6 and 10(a), uponsetting a plurality of documents G having the same sizes on the documenttray 2, the documents G are detected by an empty sensor. At the sametime, the document size is immediately detected by the size detectionsensor S1, and the document size is sent to the copy machine body H sideand set in it. By turning on the starting button of the copy machinebody H side, the feeding/reversing motor 18 and feeding clutch 17 a areoperated so that the arm 15 of the feeding roller 14 is swung, and theseparation roller 16 and feeding roller 14 are rotated to therebyseparatingly feed the uppermost one of those documents G set on thedocument tray 2.

After the leading edge of the document G is detected by the resistsensor S2, the rotation of separation roller 16 is stopped after aperiod of time t1, whereupon the leading edge of the document G isaligned by abutting the same to the resist roller 7. After standing byfor a period of time t2 after the alignment by the resist roller 7, thisroller 7 is rotated to feed the document G into the document feedingpath 6. When the document G has reached a position just upstream of theconveying roller 22 after a period of time t3, the pulse motor 25 isforwardly rotated to rotate the conveying roller 22, thereby conveyingthe document G while nipping the same between the conveying roller 22and the pinch rollers 23, 24. After a period of time t7 after theleading edge of the document G is detected by the lead sensor S3, theconveying roller 22 is stopped and thereafter stands by for scanning. Asshown in FIG. 7, the pulse motor 25 is rotated again by the readingstart signal from the copy machine body H, so that the conveying roller22 is rotated again to start the reading of the front surface ofdocument G. The rotational speed of the conveying roller 22 during thereading is controlled to be a reading speed slower than the conveyancespeed before the reading. As shown in FIG. 10(b), when the leading edgeportion of document G enters the document discharging portion 9, thisleading edge portion is detected by the document discharge sensor S5, sothat the document is discharged onto the discharge tray 37 by thedocument discharging rollers 36 which are driven to rotate by the pulsemotor 25 in a manner similar to the conveying roller 22. As shown inFIG. 10(c), the feeding of the next document G1 is started during thereading of the preceding document. After a predetermined time aftercompletion of the reading, the rotational speed of pulse motor 25 isincreased to thereby discharge the document at a higher speed, andswitched to a decreased speed discharge after a predetermined time t9,so as to complete the document discharge.

There will be explained next a double-side reading in the normal mode.In this case, there is conducted a control same with that shown in FIGS.6 and 10(a), until the scan stand-by before reading the document isperformed after the leading edge of the document G has been detected bythe lead sensor S3 and then the conveying roller 22 is just stopped. Asshown in FIGS. 8 and 11(a), after a period of time t11 from the startingof reading of document G, the feeding/reversing motor 18 drives thereversing rollers 28, and the solenoid 40 is turned on to switch bothflappers 38, 39, thereby forming a path of the document reversingportion 10 side. When the leading edge side of the document G isconveyed into the switchback path 29 to enter the switchback path 29 bypushing up the control flapper 57, this is detected by the reversesensor S4. As shown in FIG. 11(b), the document G, the front surface ofwhich has been read, is wholly moved into the switchback path 29 at ahigh speed by the conveying roller 22 after a period of time t8 from thetime of switching off of the lead sensor S3, resulting in that the rearedge of the document G becomes pinched between the reversing rollers 28.The reversing rollers 28 are then rotated in the reverse direction toswitch back the document G, to thereby feed the same with treating itsrear edge as a leading edge. At this time, the now leading edge of thedocument G abuts to a pressed contact area between the pinch roller 31and conveying roller 22, the former 31 being arranged near the outlet,whereupon the reverse alignment is conducted for a period of time t13 asshown in FIG. 11(c). Further, as shown in FIG. 2, the now leading edgeof document G is restricted by a guide 44 projectingly formed on theflapper 38, to thereby avoid contacting with the conveying roller 22, sothat the alignment of the leading edge is never obstructed. Then, duringa period of time t12 after detecting the leading edge of the document Gby the reverse sensor S4, the leading edge of the document G isintroduced to the outlet side by the control flapper 53 and the guidepiece 54, and then abutted to the pressure contact position 50 betweenthe pinch roller 31 and the conveying roller 22, thereby the alignmentis carried out. After alignment, the conveying roller 22 is rotated at ahigh speed to rapidly convey the document G up to the reading position.After the leading edge of document G is detected by the lead sensor S3,the conveying roller 22 is stopped after a period of time t16 to standby for scanning. The back surface (now front surface) of document G isread based on the reading start signal from the copy machine body Hside, and the leading edge of document G is conveyed into the documentreversing portion 10 again, as shown in FIG. 12(a). As shown in FIG.12(b), the document is wholly conveyed into the switchback path 29 ofthe document reversing portion 10 by a repeated high-speed conveyanceafter completion of reading. Thereafter, the solenoid 40 is turned offto switch both of the flappers 38 and 39 thereby forming a path towardthe document discharging portion 9, so that the document G, which hasbeen turned back to front at the document reversing portion 10, isdischarged at a high speed by the combination of the conveying roller 22and document discharging rollers 36, onto the discharge tray 37 from adocument discharge opening 34 to thereby complete the operation, asshown in FIG. 12(c). As shown in FIG. 5, the document reversing portion10 and the document feeding portion 9 are connected to each other via apath of small radius of curvature, however, a conveying force isforcibly applied in the discharge direction by means of the pinch roller31, therefore, a smooth discharge of the document can be effectedwithout reduction of conveying force. As described above, in double sidereading of documents G, the same are discharged after turning them backto front, so that the order of the documents G placed on the documenttray 2 and the order of those discharged onto the discharge tray 37 canbe corresponded to each other.

There will be described hereinafter the document reading in case of“different-size mixed mode” where different sizes of documents areplaced on the document tray 2, with reference to FIGS. 9 and 13(a). Alsoin the different-size mixed mode, the document G placed on the documenttray 2 are fed sheet by sheet by means of the separation roller 16,thereafter aligned by the resist roller 7, and conveyed toward thedocument reading portion by means of the conveying roller 22, same withthe normal mode. Different from the normal mode, the document size isnot detected by means of the size detection sensor S1 disposed on thedocument tray 2. Namely, the aligned document G is passed over thedocument reading portion without stopping there, and the leading edgeside of the document G is fed onto the discharge tray 37 as shown inFIG. 13(b). At this time, the document G is not read. In the course ofpassing of the document G over the document reading portion, the resistsensor S2 starts counting from the detection of the leading edge ofdocument G up to the detection of its rear edge, and the length ofdocument G is determined based on the counted number of times duringsuch counting, which is informed to the copy machine body H side.Further, the rotation of conveying roller 22 is stopped after a periodof time t4 after the rear edge of document G is detected by the resistsensor S2. At this time, the rear edge of document G is located at aposition which has passed over the flapper 42 of the document shuntingpath 41, as shown in FIG. 13(b). Thereafter, by conveying the document Gin the reverse direction by reversely rotating the conveying roller 22at a high speed as shown in FIG. 13(c), the rear edge of document G ismoved into the shunt path 41 with guided by the flapper 42. By reverselyconveying the document G, the lead sensor S3 detects the leading edge ofdocument G again, which means that the leading edge has reversely passedover the document reading portion 5, whereupon the conveying roller 22is stopped. Then, the conveying roller 22 is forwardly rotated tothereby feed the document G, and the stand-by is conducted afterdetecting the leading edge of document G by the lead sensor S3. Theconveying roller 22 is then forwardly rotated by obtaining the readingstart signal from the copy machine body H side, to thereby read thedocument G. The operation thereafter, i.e., from the reading of documentG up to the discharge thereof onto the discharge tray 37, is conductedin a manner same with the aforementioned one side reading in the normalmode shown in FIGS. 10(b) and 10(c). Meanwhile, there is omitted adetailed explanation about the motion of document G after the stateshown in FIG. 13(c) in the double-side reading where the document G isconveyed into the document reversing portion 10, since such operation isidentical with that of the double side reading in the normal mode asshown in FIGS. 11 and 12(a) through 12(f). Even in case of thedifferent-size mixed mode, if the rear edge of the document G isdetected by the resist sensor S2 before the leading edge is detected bythe lead sensor S3 on the upstream side of the document reading portion,the reading of document is performed based on the as-conveyed document Gin a manner similar to the normal mode, without shunting the document Ginto the document shunting path 41.

As described above, the document shunting path is formed in the documentfeeding path and in the different-size mixed mode, the length of thedocument is detected using this document shunting path, thus, there isno necessity to provide a long document feeding path as in theconventional way, to thereby achieve the minimization of the documentfeeder

Further, the document conveyance path is disposed between the documentfeeding portion and the document discharging portion positioned at thedownstream side of the document feeding portion, and branched into twopaths so that a space over the discharge tray can be used as thedocument shunting path and the further minimization of the documentfeeder can be achieved, in addition, the constitution of the documentfeeder can be simplified.

As described above, there is disposed the pinch roller for conveying thedocument with pressure contact with the conveying roller to near theoutlet of the document reversion portion, and the switchbacked documentin the document reverse portion is fed by means of the conveyance forceof the pinch roller to the document reading portion or the documentdischarging portion, so that the path structure and feeding mechanismcan be simplified and the minimization of the automatic document feederitself can be minimized.

Further, the conveyance force is forcibly applied by the pinch roller,even if the radius of curvature of the document discharge path is madesmall, a sufficient document conveyance force can be obtained.

Moreover, since the leading edge of the document fed from the documentreversing portion to the document reading portion is abutted to thepressure contact position with the conveying roller to thereby beabutted, the alignment of the leading edge of the document can beensured without an influence of the conveying roller.

Still further, there is provided the guide means for introducing theleading edge of the document fed from the document reversing portioninto the pressure contact position between the conveying roller and thepinch roller, thereby enabling the smooth alignment.

The switchback path 29 of the document reversing portion 10, as shown inFIGS. 14 and 15, is constructed by using a sealed space formed betweenthe lower surface of the discharge tray 37 and the upper surface of aplaten cover 50 for covering the platen 12. The platen cover 50 has athree layer construction of a thin aluminum plate 51 having rigidity, asponge material 52′ adhered to the lower surface of the plate 51 and asoft film 53′ covering the lower surface of the sponge material 52′. Theplaten cover 50 is rotatably supported to the automatic document feederbody J at the inner side of the switchback path 29 to have theswitchback path 29 to be able to open and close. The open and closedirection of the switchback path 29 is same as that of the automaticdocument feeder body J with respect to the copy machine body H, andtypically, the front operation panel side of the copy machine body H isconstructed to open and close.

The above platen cover 50, as shown in FIGS. 16 and 17, is attachedrotatably by means of a hinge 54′. The hinge 54′ comprises a U-shapedbracket 55 secured to the automatic document feeder body J and a fittingmember 56 secured to the rear end of the platen cover 50. The bracket 55has a front wall 55 a and a lower wall 55 b bending to the lower side ofthe front wall 55 a, and a fitting hole 57 is formed on the cornerportions of both of the walls so as to be across the walls. On the otherhand, the fitting member 56 comprises a vertical wall fitting into thefitting hole 57 and a fitting tongue 59 extending horizontally from theupper end of the vertical wall 58. The fitting tongue 59 is formed so asto be wider than the fitting hole 57 of the bracket 55 and engages withboth side edges of the fitting hole 57 to prevent the removal of thefitting member 56. Further, the fitting member 56 is fitted within thefitting hole 57 with a backlash in upper and lower directions so thatthe platen cover 50 can move in the upper and lower directions.

On the front end side of the platen cover 50 opposite to the above hinge54′, a strap or belt 60 is stretched to the automatic document feederbody J to control the opening degree of the platen cover 50. Further,provided near the belt 60 is a locking mechanism for opening and closingthe platen cover 50. As shown in FIG. 18, this locking mechanismcomprises a key member provided on the side of the automatic documentfeeder body J and a key hole 62 formed on the side of the platen cover50. The key member 61 is composed of a supporting shaft 63 projectingdownwardly and a cylindrical thumb nut 64 rotatably provided on thesupporting shaft 63. A fitting piece 65 to be engaged with the key hole62 is provided at the lower end of the thumb nut 64 so as to project outof both sides of the thumb nut 64. The opening and closing of the platencover 50 can be easily effected only by aligning the fitting piece 65with the key hole 62 to rotate the thumb nut 64 by 90°. Further,similarly as described above, the thumb nut 64 is fitted within the keyhole 62 with a backlash in upper and lower directions so that the platencover 50 can move in the upper and lower directions.

Within the above switchback path 29, ribs 66 for extending from thelower surface of the discharge tray 37 into the switchback path 29 areprovided. The ribs 66 are disposed at equal spaces along the front andrear direction of the automatic document feeder body J to serve as aguide when the document is introduced into the switchback path 29. Atthe same time, the platen cover 50 is prevented from being deformed dueto deflection by pressing down uniformly the platen cover 50 by means ofthe tips of the ribs 66 when for example, a book is put on the platen 12and covered by the platen cover 50. Further, ribs 66 a on the both sidesare formed so that a space 67 between the upper surface of the platencover 50 is narrower than that between other ribs 66 b, therebycontrolling a degree of backlash in the upper and lower directions ofthe platen cover 50.

As described above, a part of the document conveyance path is formedwithin a space region formed by the document discharging portion and thedocument cover member, and the document cover member is mounted so as tofreely open and close with respect to the document discharging portion.Thus, when a jam of the document occurs in the document conveyance path,the document cover member is opened to easily remove the jammed documentfrom the document conveyance path.

Moreover, since the open and close direction of the document covermember is the same as that of the automatic document feeder body withrespect to the platen, the open and close operation of the documentcover member can be effected from the front surface side of theoperation panel, thus the treatment is extremely easy.

The document cover member has a three layer construction having a platemember with rigidity, a foaming member attached to this plate member anda soft film member attached to this foaming member, and is mounted witha backlash in the upper and lower directions with respect to thedocument discharging portion, thereby improving the tightness to theplaten.

Since the conveyance guide projecting out of the document dischargingportion is provided in the document conveyance path, the document isconveyed along the guide to restrain the occurrence of jam and alsouniformly press down the document cover member.

Next, another embodiment will be described hereinafter. FIG. 19 shows aschematic sectional view of an automatic document feeder according tothis embodiment. In the drawings, reference numeral 1 designates anautomatic document feeder according to the present invention, whichcomprises: a document tray 2 for placing the documents thereon; documentpicking-up means 4 arranged adjacent to a document feeding opening 3; adocument feeding path 6 extending from the document feeding opening 3 upto a document reading portion 5 b which faces to document reading means5 a of a copy machine body H; a resist portion 7 provided on the way ofthe document feeding path 6 to thereby align the leading edge of thedocument; a conveying portion 8 for conveying the aligned document tothe document reading portion 5 b; a document discharging portion 9 fordischarging the document read by the document reading means 5 a; anddocument reversing portion 10 provided between the document readingportion 5 b and the document discharging portion 9. Each of thedocuments placed on the document tray 2 is fed sheet by sheet to thedocument reading portion, and the document is discharged to the documentdischarging portion 9 after its front surface is read; or switched backat the document reversing portion 10 after its front surface is read,and again fed to the document reading portion 5 b by the conveyingportion 8 to thereby read the back surface of the document.

The copy machine body H is provided with: a transparent glass 11 usedfor reading the image on the document by the document reading means 5 awhen the document is automatically fed; and a platen 12 used for readinga document such as book by having the document reading means 5 a scanmove.

The document tray 2 is arranged obliquely toward the document feedingopening 3 of the feeder body, and is provided with a guide plate 13moveable in the width direction of the documents. This guide plate 13 isto detect the width of the document, and is connected to a variableresister via a rack and a pinion gear to detect the width of thedocument based on a resistance value when the guide plate 13 moves. Thewidth of documents is detected by the position of this guide plate 13.Further, the document tray 2 is provided with three size detectionsensors S1 for detecting the length of the document in the feedingdirection. These size detection sensors S1 are constituted such as oflimit switch or optical sensor, and the size detection is performed bycombination of the guide plate 13 with the size detection sensors S1.

The document picking-up means 4 is arranged near the document feedingopening 3, and comprises: a feeding roller 14 serving as feeding meansdisplaceable in the thickness direction of the documents placed on thedocument tray 2; an arm 15 for rotatably supporting the feeding roller14; and a separation roller 16 positioned at the other end of the arm15. The feeding roller 14 is normally held in a stand-by position, andmoved from the stand-by position toward a feeding position by theoperation of a feeding clutch 17, whereafter the roller 14 is rotated byfollowing the rotation of separation roller 16 to thereby feed thedocuments on the document tray 2 sheet by sheet. There is rotated theseparation roller 16 via feeding clutch 17 which operates upon reverserotation of a DC motor (a feeding/reversing motor) 18, so that thedocuments are separated between separation pats sheet by sheet andthereafter fed to the document feeding path 6.

An empty sensor S2 is provided between the feeding roller 14 and theseparation roller 16 to detect the presence or absence of the documenton the document tray 1.

Provided on the downstream side of the above separation roller 16 is adocument feeding path 19 downwardly inclining toward a conveying roller22, and a separation sensor S3 and a resist sensor S4 are also providedin sequence. Near the downstream side of the resist sensor S4, there isprovided a resist roller 30 for effecting the alignment of the documenton the periphery of the conveying roller 22 serving as conveying means.As shown in FIG. 20, this resist roller 30 comprises a driven rollermade of resin disposed on the same shaft of a drive shaft 23 of theconveying roller 22 and a driving shaft 32 which is in pressure contactwith the driven roller 31. The driven roller 31 is disposed between eachof the conveying rollers 22 arranged along the drive shaft 23 and isformed in the substantially same size as the conveying roller 22. Thusthe driving roller 31 is in pressure contact with the driven roller 31on the substantially same surface as the periphery of the conveyingroller 22. A drive shaft 33 of the driving roller 32 is controlled by apulse motor (conveyance motor) 35 via a resist clutch 34, and alsocontrolled of its rotation by means of on/off of the resist clutch 34.The driven roller 31 is supported to the drive shaft 23 of the conveyingroller 22 so as to be able to freely rotate and the driving roller 32 isalso adapted to freely rotate when the resist clutch 34 is off. However,since the driving roller 34 applies a friction by means of a springforce, the driving roller 32 does not slip when the leading edge of thedocument abuts the resist roller 30 under a state that the clutch 34 isoff, and when the resist clutch is turned on after alignment of thedocument, the driving roller 32 rotates to send the document to theconveying roller 22 while nipping the document between the driven roller31. Thus, the resist roller 30 and the conveying roller 22 arecontrolled separately to each other, therefore, the rotation of theconveying roller 22 does not influence on the alignment of the documentat the time of alignment.

Disposed on the downstream side of the resist roller 30 is the conveyingportion 8 comprising the above conveying roller 22 for conveying thedocument while winding thereon, and auxiliary rollers 24, 25 arranged onthe periphery of the conveying roller 22. In the conveying portion 8,the document is gripped between the conveying roller 22 and theauxiliary rollers 24, 25, and fed to the document reading portion 5 bwhich is opposed to the document reading means 5 a.

There is disposed a document reading sensor S5 on the upstream side ofthe document reading portion 5 b. This document reading sensor S5 is aleading edge detecting sensor for stopping the conveyance of documentbefore reading the document. The forward conveyance of the document isresumed based on the reading start signal supplied from the copy machinebody H. The reading of document is performed by the document readingmeans 5 when the document passes over the surface of the transparentglass 11.

The document reversing portion 10 is positioned downstream of thedocument reading portion, and comprises: an introducing guide 27 with anopening thereof being flared; and a pair of reversing rollers 28disposed near the guide 27; and a switchback path 29 provided at therear side of the rollers 28. The reversing rollers 28 are opened andclosed by a DC solenoid 40, and are adapted to rotate in the forward andreverse directions by means of the DC motor 18, so that the document isreversely fed after switching back the conveyance direction of thedocument from its leading edge to its rear edge by the forward rotationand reverse rotation of the reversing rollers 28. There is disposed areverse/discharge sensor S4 near the reversing rollers 28.

The document discharging portion 9 is disposed under the document tray2, and comprises: a discharge guide 37 which bendingly extends from thedocument discharging portion 10; a pair of document discharging rollers38 provided on the way of the guide 37; and a discharge tray 39 on therear side of the rollers 38. The document discharging rollers 38 areadapted to rotate in the forward and reverse directions by means of thepulse motor 25. Disposed near the document discharging rollers 38 is adocument discharge sensor S7 for detecting the discharge of document.

There are provided a flapper 41 near the inlet of the document reversingportion 10, and a flapper 42 near the inlet of the document dischargingportion 9, respectively, for switching the conveyance direction of thedocument. The switching of these flappers 41 and 42 can be effected bymeans of the DC solenoid 43, such that the first flapper 41 switches thedocument conveyed from the document reading portion 5 b to the documentreversing portion 10, and the second flapper 42 switches the documentbetween toward the document discharging portion 9 and toward a pathextending to the document reading portion 5 b.

Next, there will be explained operations of the automatic documentfeeder of the above constitution. FIG. 21 shows a timing chart in oneside reading mode. First, upon setting documents on the document tray 2,the empty sensor S2 is turned on to detect the documents. The documentsize is immediately detected based on the size of the conveyancedirection detected by the size detecting sensor S1 and the size of thewidth direction detected from a variation of the variable volume, andthen a signal indicating the document size is sent to the copy machinebody H side. Upon turning on the starting button of the copy machinebody H side, the feeding clutch 17 is operated and after a period oftime t1, the DC motor 18 is rotated forwardly. By means of the forwardrotation of the DC motor 18, an arm 15 of the feeding roller 14 isrotated and the separation roller 16 and the feeding roller 14 arerotated to thereby separatingly feed the uppermost one of the documentsset on the document tray 2.

At the same time when the leading edge of the document is detected bythe separation sensor S3 and the resist sensor S4 due to the documentfeeding, and the rotation of the DC motor 18 is stopped after a periodof time t2 from the detection by the resist sensor S4 to thereby stopthe document feeding, the leading edge of the document abuts the resistroller 30 to be aligned. The resist clutch 34 is turned on after aperiod of time t3 from the stop of the rotation of the DC motor 18 andthe nipping conveyance by the resist roller 30 is started. The pulsemotor 35 starts rotation after a period of time t4 from the stop of therotation of the DC motor 18 and the document sent from the resist roller30 is conveyed by the conveying roller 22 and the auxiliary roller 24.

After the pulse motor 35 and the resist clutch 34 are stopped after aperiod of time t5 from when the leading edge of the document is detectedby the document reading sensor S5, the document conveyance is stopped,and thereafter stands by for reading. The pulse motor 35 is rotatedagain based on a reading start signal from the copy machine body H sothat the conveying roller 22 is rotated to send the document to thedocument reading portion 5 b, thereby starting the reading of the frontsurface of the document.

At the same time when the separation sensor S3 detects the rear edge ofthe document during the reading of the first sheet, the feeding clutch17 is turned on and the DC motor 18 starts rotation after a period oftime t6. As in the first sheet, the art 15 of the feeding roller 14 isrotated by the forward rotation of the DC motor 18 and the separationroller 16 and the feeding roller 14 are rotated to thereby separatinglyfeed the uppermost one (the second sheet) of the documents set on thedocument tray 2. As in the conveyance of the first sheet, the leadingedge of the document is detected by the separation sensor S3 and theresist sensor S4 due to the document feeding, and the rotation of the DCmotor 18 is stopped after a period of time t2 from the detection by theresist sensor S4. The feeding clutch is stopped after a period of timet3 from the stop of the rotation of the DC motor 18 and the leading edgeof the document abuts the resist roller 30 to be aligned.

At the same time when the document reading sensor S5 detects the rearedge of the first sheet, the resist clutch 34 is turned on and thesecond sheet is sent by the resist roller 30. The conveying roller 22 iscontrolled separately from the resist roller 30 and, when the secondsheet is aligned, continues the rotation to effect the readingconveyance. Therefore, even when the reading is completed, continuously,the second sheet is conveyed by the conveying roller 22 Thus, the secondsheet is aligned during the first sheet is read and conveyed, andsimultaneously with the completion of the first sheet readingconveyance, the second sheet is conveyed by the conveying roller 22,thereby improving the reduction of processing time without conveyanceloss between the documents.

The pulse motor 35 and the resist clutch 34 are turned off after aperiod of time t5 from when the leading edge of the second sheet isdetected by the document reading sensor S5 to thereby have the secondsheet stand by. During the second sheet is read after the pulse motor 35is driven again, the rear edge of the first sheet is detected by thedocument discharge sensor S7 to be discharged to the documentdischarging portion 9. During the reading of the second sheet, in thesame control as in the above, the third sheet is fed from the documenttray 2 and conveyed to the document reading portion 5 b. However, if itis judged that the second sheet is a final sheet due to the off of theempty sensor S2, as shown in FIG. 21, the leading edge detection and therear edge detection by the document discharge sensor S7 are effected andthe pulse motor 35 is turned off after a period of time t9 from thedetection of rear edge to thereby complete a sequence of automaticdocument feeding after the second sheet is discharged.

There will be explained next a timing chart of a double-side reading ofthe document with reference to FIG. 22. In this case, there is conducteda control same with that of the one side reading shown in FIG. 21, untilthe leading edge of the document is detected by the document readingsensor S3. Then, when a reading start signal is sent from the copymachine body H during standing by, the pulse motor 35 is driven and theconveying roller 22 is rotated, thereby starting the reading of thefront surface of the document. Simultaneous with the driving of thepulse motor 35, the DC solenoid is turned on to switch the flappers 41,42 to the reverse side. Also, the DC motor 18 is forwardly driven aftera period of time t6 from when the pulse motor 35 is driven, and at thesame, the reverse/discharge sensor S6 of the document reversing portion10 detects the leading edge of the document to send the document to thedocument reversing portion 10.

When the rear edge of the document is detected by the document readingsensor S5, after a period of time t7 the DC solenoid 40 is operated topress down the reversing rollers 28 for a predetermined time. Then, whenthe reverse/discharge sensor S6 detects the rear edge of the documentand the document is shunted to the switchback path 29 except for aportion pinched between the reversing rollers 28, the DC motor 18 isreversely rotated to rotate the reversing rollers 28 in the reversedirection with the reversing rollers 28 being pressed down, therebysending the reversed document from the switchback path 29 to the resistportion 7. When the resist sensor S4 detects the leading edge of thedocument as a result of the reverse conveyance of the document, after aperiod of time t2 the rotation of the DC motor 18 is stopped and thealignment of the leading edge is effected by the resist roller 30. Then,after a period of time t3, the resist clutch 34 is operated to send thedocument to the conveying roller 22.

When the leading edge of the document is detected by the documentreading sensor S5, as in the case of the reading of the front surface,the document is sent to the document reading portion 5 b after standingby for a predetermined time. The DC solenoid 40 is again turned on topress down the reversing rollers 28 after a period of time t7 from whenthe document reading sensor S5 detects the rear edge of the document.Then, when the document is again sent to the document reverse portion 10and the reverse/discharge sensor S6 detects the rear edge of thedocument, the DC motor 18 is again reversely rotated to feed thedocument from the switchback path 29, but the DC solenoid 43 is turnedoff to switch the flapper 42 to the discharge side. When the document isdischarged from the switchback path 29 as a result of the detection ofthe rear edge by the reverse/discharge sensor S6, simultaneously withthe stop of the DC motor 18, the DC solenoid 40 is turned off to releasethe pressure contact of the reversing rollers 28. While the feedingclutch 17 is turned on to start the feeding of the second sheet after aperiod of time t8 after the detection of the rear edge by thereverse/discharge sensor S6, the document discharge sensor S7 detectsthe rear edge of the document, the document is put on the discharge tray39 and the pulse motor 35 is stopped after a period of time t9 from thedetection of rear edge to complete the discharge of the first sheet.Additionally, the conveyance control for the second and succeedingsheets is effected in the same timing. Further, the documents in theoriginal page sequence are received in the discharge tray 39.

What we claimed are:
 1. An automatic document feeder comprising: adocument feeding portion for feeding a document placed thereon; adocument reading portion at which an image of said document is read; adocument discharging portion for discharging said document of which saidimage has been read; a document feeding path for guiding said documentbetween said document feeding portion and said document reading portion;a document discharging path arranged with at least a part thereofoverlapped with at least a part of said document feeding path in avertical direction, for guiding said document between said documentreading portion and said document discharging portion; a documentshunting path arranged with at least a part thereof arranged between atleast a part of said document feeding path and at least a part of saiddocument discharging path in a vertical direction such that at least apart of each of said document shunting path, said document feeding pathand said document discharging path are overlapped in said verticaldirection, and wherein said document shunting path is branched from saiddocument feeding portion; and conveying means for conveying saiddocument in a forward direction along said document feeding path fromsaid document feeding portion to pass a leading edge of said documentthrough said document reading portion, then conveying said document in areverse direction along said document feeding path toward said documentshunting path so that at least another edge of said document isaccommodated in said shunting path, and thereafter conveying saiddocument in the forward direction along said document feeding path to bepassed through said document reading portion, and further, conveyingsaid document in the forward direction along said document dischargingpath to be discharged to said document discharging portion.
 2. Anautomatic document feeder according to claim 1, wherein the overlappingin the vertical direction of said document feeding path, said documentdischarging path and said document shunting path is provided on saiddocument feeding portion side with respect to said document readingportion.
 3. An automatic document feeder according to claim 1, furthercomprising a size detector for detecting a document size before theleading edge of said document reaches said document reading portion fora second time.
 4. An automatic document feeder according to claim 3,wherein said size detector is provided to said document feeding path todetect the leading edge and a rear edge of said document.
 5. Anautomatic document feeder according to claim 1, further comprising: afirst detector provided to said document feeding path between a junctionof said document feeding path and said document shunting path, and saiddocument reading portion, for detecting a rear edge of said documentbeing conveyed along said document feeding path, wherein said conveyingmeans switches the conveying direction of said document being conveyedin the forward direction along said document feeding path to the reversedirection based on a detection result by said first detector.
 6. Anautomatic document feeder according to claim 1, further comprising: asecond detector provided to said document feeding path on the upstreamside in the forward conveying direction of said document with respect tosaid document reading portion, for detecting the leading edge of saiddocument, wherein said conveying means switches the conveying directionof said document again to the forward direction, based on the detectionof leading edge by said second detector when said document is beingconveyed in the reverse direction at said document reading portion. 7.An automatic document feeder according to claim 1, further comprising: afirst detector provided to said document feeding path between a junctionof said document feeding path and said document shunting path, and saiddocument reading portion, for detecting a rear edge of said documentbeing conveyed along said document feeding path; and a second detectorprovided to said document feeding path on the upstream side in theforward conveying direction of said document with respect to saiddocument reading portion, for detecting the leading edge of saiddocument, wherein said conveying means switches the conveying directionof said document being conveyed in the forward direction along saiddocument feeding path to the reverse conveying direction based an adetection result by said first detector, and thereafter, switches theconveying direction of said document again to the forward directionbased on a detection result by said second detector.
 8. An automaticdocument feeder according to claim 1, further comprising: a firstdetector provided to said document feeding path, for defecting saidanother edge of said document being conveyed along said document feedingpath; and a second detector provided to said document feeding pathbetween said first detector and said document reading portion, fordefecting said leading edge of said document, wherein said conveyingmeans switches the conveying direction of said document to accommodatesaid another edge of said document in said shunting path, if said seconddetector detects said leading edge of said document before said firstdetector detects said other edge of said document being conveyed in theforward direction from said document feeding portion.
 9. An automaticdocument feeder according to claim 1, wherein: said automatic documentfeeder enables the use of various sized documents; and a conveying pathincluding said document feeding path and said document discharging pathcomprises a U-shaped path shorter than a length in the conveyingdirection of a largest sized document among said various sizeddocuments.